Negative commands in Spanish are used to tell someone not to do something. They are formed similarly to formal commands by dropping the 'o' from the verb's infinitive form, adding the opposite ending, and placing "no" before the verb. Some common irregular verbs in the negative command form are "no vayas", "no des", "no seas", "no hayas", and "no estes". Examples of negative commands include "no me hables asi", "no comas tanto", and "no conduzcas rapido".